The invention relates to postage meters, and more particularly to flat-bed printing meters, and to security and control devices therefor.
Electronic meters of the flat-bed printer type are well-known and are described for example in U.S. Pat. No. 4,579,054, issued to Buan, et al. which shows a stand-alone electronic mailing machine in which the electronic postage meter forms an integral part of the device. Other aspects of such a stand-alone mailing machine are described in U.S. Pat. Nos. 4,535,407 and 4,523,523, among others.
Of particular concern in postage meters and mailing machines is the prevention of unauthorized printing of a meter impression (postage indicium). That is, since the printing of the postage indicium assumes that the Post Office has been paid for the delivery of the mailpiece, printing of the postage indicium without accounting for its value will result in loss of revenue to the Post Office to cover the costs of delivery. It will be appreciated that in an area of such concern, many devices have been developed to solve problems associated with the security of the printing die.
Die protection assemblies incorporate various mechanical arms of projections which protrude from the printwheel area of the die in order to prevent a person from simply placing an envelope against the die to obtain an imprint.
U.S. Pat. No. 2,795,186, issued to Bach, shows a movable shroud which can be lowered to guard the printing die against taking unauthorized impressions at any time between printing operations. The shroud completely covers the face of the value printing die when the printing mechanism is not in an operating cycle and is locked in that position until the cycle starts at which time the shroud is moved to a position uncovering the die. U.S. Pat. No. 4,559,444 issued to Erwin, et al. teaches an interposer arrangement which extends upward from the platen into the space into which an envelope or other workpiece is to be inserted. These interposers are moved out of the way during a legitimate printing operation. The interposer blades are mechanically linked to the inking mechanism in order to move the blades out of the way as the mailpiece moves into position for imprinting. U.S. Pat. No. 4,796,527 describes an interposer device which is linked to the motor driving the platen of the printer to move out of the way or is actuated by a power switch to be moved out of the way so long as power is applied to the machine.
While these known devices work well in the particular environments in which the platen and the die are not expected to be physically separated, in a modular device where the platen is retained, several new security and control issues are created in respect of a flat-bed printer type of postage meter. Accordingly, U.S. Pat. No. 5,049,727, issued to Abellana, et al, describes a postage meter having a moveable shutter which is driven by a drive mechanism between a first position which covers the postage meter printing die and a second position which permits the printing die to be exposed through an opening in the postage meter base to permit printing of a postage indicia. The shutter bar drive mechanism also serves the function of unlatching the postage meter from a locked position so that it can be removed from its associated mailing machine for inspection, repair, or to permit access to certain mailing machine components.
While the shutter bar drive mechanism of U.S. Pat. No. 5,049,727 has performed admirably over the years, its design is such that, under certain circumstances, it is possible the shutter bar will become cocked and bind or alternatively result in only a partial unlocking of the postage meter from the mailing machine. Thus, what is needed is an improved drive mechanism for a shutter bar of a postage meter having a flat-bed printer which overcomes the problems of the drive mechanism described in U.S. Pat. No. 5,049,727.